【名词&注释】
垃圾邮件(spam)、被子植物(angiosperm)、木质部(xylem)
[单选题]珠被常为( )。
A. 一层
B. 二层
C. 三层
D. 一层或二层
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举一反三：
[单选题]DWhen I first got an email account ten years ago, I received communications only from family,friends,and colleagues.Now it seems that every time I check my e-mail ,I have an endless seriers of advertisement and otner correspondence that do not interest the at all.If we want e-mail to continue to be useful,we need special laws that make spamming(发送垃圾邮件) a crime.
A. This problem is troubling for inviduals and companies as well. Many spam emails contain computer viruses that can shut down the entire network of a company.Companies rely on e-mail on on e-mail for their Comployees to communicate with each other. Spam frequently causes failures in their local commnications networks,and their employees are thus unable to communicate effectively.such a situationg results in a loss of productivity and requires companies to repeatedly repai their networks.These computer problems raise productton costs of companies ,which are,in the end,passed on to the consumer.
B. 60.What is the purpose of the text?
C. To inform.
D. To educate
E. To persuade
F. To instruet
[多选题]被子植物的木质部是由( )构成的。
A. 导管
B. 筛管
C. 管胞
D. 木纤维
E. 木薄壁细胞
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